double a,b,c,d,e,f,x,y,z,s,r;main(){for(;~scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f);){x=hypot(a-c,b-d);y=hypot(a-e,b-f);z=hypot(c-e,d-f);s=(x+y+z)/2;printf("%.2lf\n",2*3.141592653589793*x*y*z/(4*sqrt(s*(s-x)*(s-y)*(s-z))));}}
